Recently in the automotive industry, electric motors have been replacing power steering hydraulic pumps because of the requirements for electronic stability control and roll prevention systems and better fuel efficiency (i.e. engine power reduction). The main steering angle sensor for such electric motors needs to be a multi-turn rotary position sensor.
Present steering angle sensing techniques include optical encoders with multi-turn counters that require specialized algorithms to combine the turn counter code to the single turn optical encoder information. Another technique used is a gear reduction ratio (in this application, 5:1) technique to convert a multi-mechanical turn into a single turn rotation. However, this method degrades the resolution and linearity accuracy performance of the sensor. By way of example, a sensor with 1% of linearity error will be converted to a 5% error due to the 5:1 gear reduction ratio, and a step size of 0.01 degree in a single-turn unit becomes 0.05 degree/step in a five-turn unit.
Therefore, it is desirable to provide a multi-turn rotary position sensor that has better resolution and linearity accuracy performance for automotive and other applications.